# US 11,112,472 B2 · Pre-emphasis techniques based on temperature dependent gradient system behavior for trajectory correction in magnetic resonance imaging

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- Number: US 11,112,472 B2
- Document ID: US11112472B2
- Status: Granted
- Kind: B2
- Application number: 16/699,415
- Filed: 2019-11-29
- Published: 2020-10-22
- Granted: 2021-09-07
- Earliest claimed: 2019-04-18
- Assignees: Siemens Healthcare GmbH; Julius-Maximilians-UniversitäT WüRzburg; The United States of America, as represented by the Secretary, Department of Health and Human Services
- Applicants: Gudrun Ruyters; Andrew Dewdney; Manuel Stich; Herbert Köstler; Christiane Pfaff; Tobias Wech; Adrienne Campbell
- Inventors: Gudrun Ruyters; Andrew Dewdney; Manuel Stich; Herbert Köstler; Christiane Pfaff; Tobias Wech; Adrienne Campbell
- Web page: https://patentgrep.com/patent/US11112472B2

## CPC

- G01R 33/3856: {Means for cooling the gradient coils or thermal shielding of the gradient coils}
- G01R 33/3852: {Gradient amplifiers; means for controlling the application of a gradient magnetic field to the sample, e.g. a gradient signal synthesizer}
- G01R 33/56572: {caused by a distortion of a gradient magnetic field, e.g. non-linearity of a gradient magnetic field (G01R33/56509, G01R33/56518, G01R33/56536 take precedence)}
- G01R 33/56518: {due to eddy currents, e.g. caused by switching of the gradient magnetic field}
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)

## Abstract

A gradient system characterization function (e.g., a gradient system transfer function) may be developed by measuring a behavior of the MR device at a target temperature and developing at least one gradient system characterization function for a gradient coil of a magnetic resonance (MR) device at the target temperature based on the measured behavior. A patient may be subsequently imaged by the MR device, wherein the imaging process comprises measuring a temperature of a gradient coil, determining a gradient system characterization function at the measured temperature, calculating a pre-emphasized gradient of the gradient coil, and imaging the patient using the pre-emphasized magnetic field component.

## Claims

### Claim 1

A method for developing at least one gradient system characterization function for a magnetic resonance (MR) device, the method comprising:
setting at least one gradient coil of the MR device at a target temperature;
measuring a behavior of the MR device at the target temperature at different frequencies of the at least one gradient coil, wherein the different frequencies are generated by varying current through the at least one gradient coil; and
developing, by a processor of the MR device, at least one gradient system characterization function for the at least one gradient coil of the MR device at the target temperature based on the measured behavior.

### Claim 2 (depends on 1)

The method of claim 1, wherein the gradient system characterization function is a gradient system transfer function.

### Claim 3 (depends on 2)

The method of claim 2, wherein the gradient system transfer function is developed for a zeroth order, first order, second order, third order field term, or a combination thereof.

### Claim 4 (depends on 1)

The method of claim 1, further comprising:
repeating the setting, the measuring, and the developing for at least one additional target temperature to provide a plurality of gradient system characterization functions for the at least one gradient coil of the MR device at a plurality of target temperatures; and
storing the plurality of gradient system characterization functions in a database of the MR device.

### Claim 5 (depends on 4)

The method of claim 4, wherein the plurality of target temperatures is predetermined by an operating temperature range of the MR device.

### Claim 6 (depends on 4)

The method of claim 4, wherein the plurality of gradient system characterization functions is a plurality of gradient system transfer functions,
wherein the at least one gradient coil comprises a first gradient coil for an x-axis, a second gradient coil for a y-axis, and a third gradient coil for a z-axis of the MR device,
wherein the behavior of the MR device is measured independently for each gradient coil at each target temperature, and
wherein a gradient system transfer function is developed for each axis of the MR device at each target temperature of the plurality of target temperatures.

### Claim 7 (depends on 1)

The method of claim 1, wherein the setting of the target temperature comprises heating at least one gradient coil by running an electrical current through the at least one gradient coil.

### Claim 8 (depends on 1)

The method of claim 1, wherein the target temperature of the MR device is monitored by at least one temperature sensor associated with a respective gradient coil.

### Claim 9

A method of imaging a patient using a magnetic resonance (MR) device, the method comprising:
measuring a temperature of at least one gradient coil of the MR device using at least one temperature sensor associated with the respective gradient coil;
determining, using a processor of the MR device, a gradient system characterization function for the at least one gradient coil based on the measured temperature of the respective gradient coil;
calculating a pre-emphasized gradient for the at least one gradient coil using the determined gradient system characterization function; and
imaging the patient using the pre-emphasized gradient.

### Claim 10 (depends on 9)

The method of claim 9, wherein the at least one temperature sensor comprises a plurality of temperature sensors, and
wherein the measured temperature of the respective gradient coil is based on temperature measurements for more than one temperature sensor of the plurality of temperature sensors.

### Claim 11 (depends on 9)

The method of claim 9, wherein the determining of the gradient system characterization function comprises:
retrieving, from a database of the MR device, at least one stored characterization function for the respective gradient coil, each stored characterization function based on a measured behavior of the MR device at a target temperature at different frequencies of the respective gradient coil which has been generated by through a varying of current through the respective gradient coil; and
modeling, by the processor, the gradient system characterization function using the at least one stored characterization function and any temperature difference between the measured temperature of the respective gradient coil and the target temperature of a respective stored characterization function.

### Claim 12 (depends on 11)

The method of claim 11, wherein the modeling comprises interpolating the gradient system characterization function for the measured temperature between a first stored transfer function at a target temperature greater than the measured temperature and a second stored characterization function at a target temperature less than the measured temperature.

### Claim 13 (depends on 11)

The method of claim 11, wherein the modeling comprises extrapolating the gradient system characterization function for the measured temperature from at least two stored characterization functions having target temperatures that are either greater than or less than the measured temperature.

### Claim 14 (depends on 9)

The method of claim 9, wherein the at least one gradient coil comprises a plurality of gradient coils including a first gradient coil for an x-axis, a second gradient coil for a y-axis, and a third gradient coil for a z-axis of the MR device,
wherein temperatures are measured for each gradient coil of the plurality of gradient coils,
wherein gradient system characterization functions are determined for each gradient coil of the plurality of gradient coils,
wherein pre-emphasized gradients are calculated for each gradient coil of the plurality of gradient coils, and
wherein the patient is imaged using the pre-emphasized gradients for the plurality of gradient coils.

### Claim 15 (depends on 9)

The method of claim 9, wherein the gradient system characterization function is a gradient system transfer function.

### Claim 16 (depends on 15)

The method of claim 15, wherein the pre-emphasized gradient is a first order magnetic field term calculated using the following formula:
gpre,1T(t)=−1{Gnom,l(f)·GSTFl,lT−1(f)}
wherein:
gpre,lT(t)=the pre-emphasized gradient for direction l and Temperature T,
=Fourier transform,
Gnom,l(f)=nominal uncorrected gradient at frequency f, direction l (for a reference temperature state, and
GSTFl,lT−1(f)=gradient system transfer function at the frequency f and the direction l (for a specific temperature state T).

### Claim 17 (depends on 9)

The method of claim 9, further comprising:
reconstructing an image of the patient, wherein the reconstructed image comprises a reduced number of artifacts in comparison to a MR image acquisition process without use of the pre-emphasized gradient in the imaging.

### Claim 18

A magnetic resonance (MR) device comprising:
a plurality of gradient coils having a first gradient coil for an x-axis, a second gradient coil for a y-axis, and a third gradient coil for a z-axis of the MR device;
at least one temperature sensor for each gradient coil of the plurality of gradient coils, the at least one temperature sensor configured to monitor a temperature of the respective gradient coil;
at least one processor configured to set at least one gradient coil to a target temperature, measure a behavior of the MR device for the at least one gradient coil at different frequencies generated by varying current through the at least one gradient coil, and develop at least one characterization function for the at least one gradient coil at the target temperature based on the measured behavior; and
a database or non-transitory memory configured to store the at least one characterization function of the at least one gradient coil of the plurality of gradient coils.

### Claim 19 (depends on 18)

The MR device of claim 18, wherein the characterization function is a transfer function.

### Claim 20 (depends on 18)

The MR device of claim 18, wherein the at least one characterization function comprises a plurality of characterization functions for a plurality of target temperatures for each gradient coil of the plurality of gradient coils, and
wherein the plurality of target temperatures is predetermined by an operating temperature range of the MR device.

### Claim 21 (depends on 18)

The MR device of claim 18, wherein the at least one processor is further configured to:
measure an operating temperature of at least one gradient coil of the plurality of gradient coils;
determine a gradient system characterization function for the at least one gradient coil based on the measured operating temperature of the respective gradient coil and the at least one characterization function of the respective gradient coil stored in the database;
calculate a pre-emphasized gradient for the at least one gradient coil using the determined gradient system characterization function; and
image a patient using the calculated pre-emphasized gradient.

### Claim 22 (depends on 21)

The MR device of claim 21, wherein the gradient system characterization function is a gradient system transfer function.

### Claim 23 (depends on 21)

The MR device of claim 21, wherein the determining of the gradient system characterization function comprises modeling the gradient system characterization function using the at least one stored characterization function and any temperature difference between the measured operating temperature of the respective gradient coil and the target temperature of a respective stored characterization function.

### Claim 24 (depends on 18)

The MR device of claim 18, wherein the processor is further configured to reconstruct an image of a patient to provide a reconstructed image,
wherein the reconstructed image comprises a reduced number of artifacts in comparison to a MR image acquisition by the MR device without use of pre-emphasized magnetic field components in the imaging.